September 15th, 2017: This has been a proud day that will be forever etched in the history of space exploration. The Cassini orbiter, explorer of Saturn and its icy moons for more than 20 years will today accomplish its mission. It is running out of fuel. So to protect the moons of Saturn where there is a possibility of life NASA, planned a spectacular farewell to this magnificent explorer. The Cassini orbiter dives into the atmosphere of Saturn at 7:55:46 A.M. EDT leaving behind its legacy of being one of the finest explorer spacecraft ever sent by NASA.
The Cassini-Huygens space missions, or simply Cassini was a collaborative project between the National Aeronautics Space Administration (NASA), the European Space Agency ESA, and the Italian Space Agency (ASI) to send a spacecraft to explore Saturn, its rings and its moons which are expected to sustain life in some form. The spacecraft contained both the Cassini space probe and the European Huygens lander which landed on the largest moon of Saturn- Titan.
History
The cassini was originally conceptualized in the early 1980s when the European Science Foundation, and the American National Academy of Sciences, formed a collaboration and it was decided that a joint project consisting of a Saturn Orbiter and a Titan lander.
NASA and the ESA performed studies that could give information about potential missions, in 1984 and 1985. While the European Space Agency continued with its research, NASA astronaut Sally Ride presented NASA Leadership and America’s Future in Space: A Report to the Administrator or the Ride Report in 1987.
The Ride report suggested four areas of study:
- A mission to Earth
- Exploration of the Solar System
- Outpost on the Moon
- Humans to Mars.
Each of them provides a significant direction to study our Solar System, and our planet. The section “Exploration of Solar System” of the Ride Report gave the green light to the Cassini mission, but as a solo NASA mission. However in 1988 Len Flisk, NASA’s Associate Administrator of Space Science and Applications contacted his European counterpart at ESA, Roger Bonnet, for moving forward with a joint NASA and ESA venture to explore Saturn and its moons. In the later half of 1988 ESA approved Cassini-Huygens missions as its next major mission in collaboration with NASA.
Now that all the funding, political and other works of public relation was under way. The focus was to be concentrated on the actual development of the spacecraft. NASA and ESA were joined by teams from several different countries which consisted of ASI, the Italian Space Agency. Task was humongous; integrating 5000 scientists from 17 different countries to explore this giant situated 1.6 billion kilometers from Earth. While the actual distance of travel would be compounded many fold as there is no straight travel path in space.
Cassini Lifts Off
October 15th, 1997, the launch day. Huygens was attached to the Cassini orbiter and they were both shielded and secured in the spacecraft. Experts and scientists make the final measurements, re-checking each part of the orbiter and the lander. Cassini is launched from the Cape Canaveral Air Force Station’s Space Launch Complex 40, Florida with the help of Titan IV-B (Centaur) rocket launcher. Because of the distance of Saturn from the Earth, Solar Array was not feasible choice hence the Cassini orbiter was powered by 3 GPHS-RTG radioisotope thermoelectric generators, which use heat from the decay of about 33 kg of plutonium-238 to generate DC current electricity via thermoelectrics. The orbiter travelled with gravity assists from Venus, Earth and Jupiter, a method to minimize the fuel consumption.
Huygens Lander
The Huygens probe named after Dutch Astronomer Christiaan Huygens, who was credited as the first discoverer of the Saturn’s moon Titan, was a space probe designed to land on Titan. It was developed and operated by the European Space Agency, and was a part of the joint venture between NASA and ESA, the Cassini-Huygens mission. It was mated to the Cassini orbiter during its launch from Cape Canaveral. Huygens was separated from Cassini on December 25, 2020, and landed on Titan on January 14 the following year near the Adiri region of Titan. The main purpose of the lander was to send atmospheric, and surface data back to the earth.
The Two Venus Flybys
The Cassini orbiter arrived at Venus for a gravity assist flyby for the first time on April 25, 1998. It gained enough acceleration to go ahead in its path. Nearly after fourteen months, it completed its revolution around the sun, and approached venus for its second assisted flyby.
The Earth Flybys
After nearly two years of leaving home, the cassini approached and performed a gravitational-assist flyby of the Earth on August 18, 1998, bidding adieu to its home forever. This flyby was very risky according to mission standards, as a manoeuvring failure could have resulted in thousands of deaths due to its radioactive fuel Plutonium-238 Oxide. But everything went smoothly, accelerating Cassini to reach the asteroid belt where it again made a flyby of the 2685 Masursky, an asteroid, on January 23, 2020. During its five months of journey through the asteroid belt it uses its Cosmic Dust Analyzer (CDA) to study the dust particles in the region as well.
Crossing the Jupiter
A little more than three years from its launch date Cassini makes its closest approach to Jupiter on December 30, 2020. It teamed up with Galileo space orbiter to take around 26,000 images of Jupiter, its faint ring and moons, during a six months flyby providing the most detailed portrait of the planet till date. After this, Cassini was set on the final frontier of its voyage proceeding to Saturn. The Cassini detected two huge storms brewing on Saturn and finally merging into one, just three months before reaching Saturn. It was a rare phenomenon, only observed once before this.
Apart from exploration of Saturn, it was credited with many important discoveries. Seven new moons orbiting Saturn were discovered by this majestic explorer in its total lifetime. This includes discovery of Methone, Polydeuces, and Pallene in 2004, Daphinis on May 1, 2005, and Anthe on May 30, 2007.Finally, in 2009 it discovered two other moons Aegaeon in the G-ring system, and the provisionally named propeller moonlet S/2009 S 1 in the B-ring system. Although the photographs from Voyager 2 later revealed that Pallene was indeed discovered by Voyager 2 long before Cassini did.
June 30, 2004
After a journey of 7 long years from Earth, Cassinifinally reached Saturn on June 30, 2020. It enters the Saturnarian orbit, moving towards Titan. Upon reaching Titan another important event would take place integral to the Cassini- Huygens mission, where the European friend of Cassini, the Huygens lander will be separated from Cassni.
GoodBye Huygens !
On Christmas Day 2004, Cassni released the Huygen lander, which entered the Titan’s atmosphere on January 14, 2005. Assisted by 3 parachutes Huygens descends for 150 minutes before landing on the Titan’s surface. But everything did not go according to the plan. Due to a system failure, the 350 pictures taken during Huygens’ descent could not be relayed back to Earth.
Exploring Enceladus
Cassini was very successful in its exploration of the moon Enceladus, the sixth largest moon of Saturn. Its exploration by Cassini revealed a thin atmosphere, consisting of ionized water vapour that constituted 91% of its atmosphere, 4% nitrogen, 3% carbon dioxide and 1.7% methane, and traces of other hydrocarbons. It also captured Enceladus’s south pole icy geysers erupting.
Exploration Continues
Cassini continued exploring the rings of the Saturn, through radio occultation to measure the Saturnian atmosphere and size of the particles in the rings of the saturn. Imaging of its ring verified that the rings of Saturn indeed had spokes. It also captured unknown bands in the ring. During this period the Cassini witnessed many rare phenomena, one of them being the Equinox, the phenomenon in which Sun’s rays fall tangentially on the rings, making the rings disappear.
The Grand Finale: Plunging into the Saturnian Atmosphere.
By 2017, Cassini was running out of fuel. This posed a big question: ‘What should be done to mark the end of the mission?’ It was always risky as crashing unto any of the moon could lead to contamination of the moon, destroying possible signs of habitability.
So, it was decided that Cassini enters the atmosphere of Saturn, where it merges into the atmosphere. Cassini flew by the gap between the cloud top of Saturn and its innermost ring. This gap is about 1500 miles. The dive lasted for almost a day, 20 hours to be precise. After that Cassini established its connection with Earth relaying its last journey into the Saturnian atmosphere. Below is the video of the Grand finale of Cassini by Nat Geo. Do enjoy.